^38 



NATURE 



[April 17, 19 19 



•the native industry carried on in Madras, Dr. Marsden 

 points out that the difficulties are much more formid- 

 able, and he suggests that the first step towards 

 improvement must be the provision of means for 

 the production of indigo of good and uniform 

 quality. One means to this end would be the 

 replacement of small-scale manufacture in native- 

 owned vats by larger-scale production in well-managed 

 factories, the ryot selling his crop to the factory for 

 manufacture into dyestuff. A possible alternative rnay 

 be the elaboration of a simple process, capable of being 

 used by the ryot, as the result of the researches now 

 being carried on by Mr. Davis, coupled with some 

 system of analytical control of the produce before ship- 

 ment. 



VSES OF INVISIBLE LIGHT IN 

 WARFARE. 



FROF. R. W. WOOD, of Johns Hopkins Univer- 

 sity, Baltimore, gave to the Physical Society of 

 London on March 14 a demonstration of the uses of 

 invisible light in warfare. The first device shown was 

 a signalling-lamp, consisting of a 6-volt electric lamp 

 with a small curled-up filament at the focus of a lens 

 of about 3 in. diameter and 12 in. focus. This gave 

 a very narrow beam, only visible in the neighbourhood 

 of the observation post to which the signals were 

 directed. In order to direct the beam in the proper 

 direction, an eyepiece was provided behind the fila- 

 ment. The instrument was thus converted into a 

 telescope, of which the filament served as graticule. 

 When directed so that the image of the observation 

 post was covered by the filament, the lamp, when lit, 

 threw a beam in the proper direction. In many cir- 

 cumstances the narrowness of the beam was sufficient 

 to ensure secrecy ; but sometimes it was not desirable 

 to show any light whatever, and filters were employed 

 to cut out the visible spectrum. By day a deep red 

 iilter, transmitting only the extreme red rays, was 

 placed in front of the lamp. The light was invisible 

 to an observer unless he was provided with a similar 

 red screen to cut out the daylight, in which case he 

 could see enough to read signals at six miles. By 

 night a screen was used which transmitted only the 

 ultra-violet rays. The observing telescope was pro- 

 vided with a fluorescent screen in its focal plane. 

 The range with this was also about six miles. For 

 naval convoy work lamps are required which radiate 

 in all directions. Invisible lamps for this purpose 

 were also designed. In these the radiator was a ver- 

 tical Cooper-Hewitt mercury arc, surrounded by a 

 chimnev of the ultra-violet glass. This glass only 

 transmits one of the mercury lines, viz. A = 366o A.U., 

 which is quite beyond the visible spectrum. Neverthe- 

 less, the lamp is visible at close quarters, appearing 

 of a violet colour, due to fluorescence of the retina. 

 The lens of the eye is also fluorescent. This gives 

 rise to an apparent haze, known as the "lavender 

 fog," which appears to fill the whole field of view. 

 Natural teeth also fluoresce quite brilliantly, but false 

 teeth appear black. 



Reverting to the use of the lamps at sea, they are 

 picked up by means of a receiver consisting of a 

 condensing lens In the focal plane of which Is a 

 barlum-platlno-cyanlde screen the full diameter of the 

 tube. An eyepiece Is mounted on a metal strip across 

 the end of the tube. When the fluorescent spot has 

 once been found somewhere on the screen, it is 

 readilv brought to the central part and observed with 

 the eveplece. The range Is about four miles, and the 

 arrangement has proved Invaluable for keeping the 

 ships of a convov together In their proper relative 

 positions by night. 



NO. 2581, VOL. 103] 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 

 London. — A course of eight lectures on "The 

 Physiologv of Muscular Exercise" will be given in 

 the Phvs'iological Department, St. Bartholomew's 

 Hospital' Medical School, West Smithfield, E.C.i, by 

 Prof. F. A. Bainbridge on Wednesdays at 4.30 p.m., 

 beginning on April 30. The course is intended for 

 advanced students of the University and others in- 

 terested in the subject. Admission is free, without 

 ticket. 



We learn from Science that by the will of the late 

 Mr. Morton F. Plant the Connecticut College for 

 Women receives a bequest of 50,000?. 



Sir Arthur Newsholme has been offered the chalr 

 of public health at Johns Hopkins University, Balti- 

 more, and It Is understood that he will accept the 

 offer for a year at least. 



The sixth election to Beit fellowships for scientific 

 research will take place on or about July 15. Not 

 more than three fellowships, of the value of 175L per 

 annum, will be awarded. Applications must be re- 

 ceived on or before May 31. Forms of application 

 and all information may be obtained, by letter only, 

 addressed to the Rector, Imperial College, South 

 Kensington. London S.W.7.- 



By the will of the late Mr. Charles Kerr Marr, the 

 residue of his property, amounting apparently to more 

 than 200.000Z. . Is left In trust for educational pur- 

 poses, defined as follows :—" For granting prizes or 

 rewards to persons who are or have been bona-fide 

 residents In the borough of Troon, and who are or 

 have been scholars In some public or elementary 

 school : in or towards building or maintenance of 

 anv public school, elementary or otherwise, in Troon; 

 In or towards the maintenance of exhibitions or 

 scholarships tenable at any institution of education 

 higher than elementary, as the trustees mav deter- 

 mine, but no exhibition or scholarship shall be 

 awarded to anv person who shall not be or have been 

 a hona-fide resident in Troon." 



In the Issue for April 5 of the Cologne Post, a daily 

 paper published at Cologne by the Army of the 

 Rhine, is an article on the education of A Iv. boys. 

 The writer states that the boys of eighteen years of 

 age who have been called to the colours recently 

 have. In the majority of cases, proved to be vastly 

 below the standard of education to be expected of 

 boys of that a£fe, as many as 5 per cent, of them 

 being quite Illiterate. He goes on to advocate the 

 Institution of a system of vocational education while 

 the bovs are with the Army of Occupation that will 

 return these lads to their civil occupations each one 

 w^Ith his studies completed and with his " apprentice- 

 ship " served. The curriculum and time-table of 

 studies sketched In the article indicate a due apprecia- 

 tion of the difficulties of the problem and the possi- 

 bility of overcoming them successfully. 



The Cologne Post of April i publishes an interest- 

 ing account of the work of the 2nd Arm}' Agricul- 

 tural College at Bonn. The object of the college is 

 to provide Interesting and useful occupation for our 

 troops during the period preceding demobilisation. 

 Courses were commenced in January, iqig, since 

 which time large numbers of soldiers, both officers 

 and other ranks, have received short courses of agri- 

 cultural instruction. At first the lectures were malnlv 

 theoretical, dealing with agricultural chemistry and 

 botany, but this was soon altered, and at the present 

 time the students not only have lectures on practical 

 subjects — farm management, etc.- — but are also 



